Compact multicast switches, mxn switches and mxn splitters

ABSTRACT

New architectures for multicast switches, and other optical switches and splitters, that have substantially reduced insertion loss, crosstalk and better overall optical performance in comparison to existing optical switches and splitters. Optimized waveguide mesh layouts are used to substantially reduce the number of waveguide crossings, which reduces insertion loss. The reduction in the number of crossings also reduces the complexity of the mesh and provides better crossing angles to reduce crosstalk and other issues. Instead of crossing all of the waveguides connected between splitter outputs and switch inputs, the waveguides are crossed in sets of waveguides.

FIELD OF THE INVENTION

Embodiments of the invention relate to optical network switches andsplitters and, more particularly, to multicast switches, M×N switchesand M×N splitters used in optical networks.

BACKGROUND

As technology advances, there is a need for optical networks to becomecolorless, directionless, and contentionless (CDC). These types ofnetworks require new colorless optical components that can re-route anyoptical signal from any input node to any output node.

An M×N multicast switch (MCS) is one of the components suitable for usein a CDC network. A typical M×N multicast switch 10 is illustrated inFIG. 1. As can be seen, the multicast switch 10 comprises a number M of1×N splitters 12 ₁, . . . , 12 _(M) (collectively “splitters 12”) forsplitting up optical signals received via M inputs to the switch 10. Themulticast switch 10 also comprises a number N of M×1 switches 14 ₁, . .. , 14 _(N) (collectively “switches 14”) for collecting signals from theoutput of the splitters 12 and outputting the signals to selected onesof N outputs from the switch 10. A control mechanism (not shown) ensuresthat the switches 14 are set to output the correct signal.

It is known that PLC (planar lightwave circuit) technology is wellsuited for implementing the M×N multicast switch 10, as both thesplitters 12 and switches 14 can be fabricated with good opticalperformance. However, and as can be appreciated, the difficulty arisesin how to get all of the splitter 12 outputs connected to theappropriate inputs of all of the switches 14 without impacting theoptical performance of the switch 10 and without making the switch 10too large, complex or costly. The problem is compounded for largerswitches 10 as the number of splitter 12 outputs and switch 14 inputsincreases exponentially.

FIG. 1 illustrates the outputs of splitter 12 ₁ and 12 _(M) as beingconnected to certain inputs of the switches 14. As mentioned above, allof the splitter 12 outputs would need to be connected to appropriateinputs of all of the switches 14. Optical waveguides can be used forthis purpose and are a viable solution to the connection problemdescribed above. In one form, optical waveguides can be implemented as amesh of light paths formed within the substrate containing the splitters12 and switches 14. As can be seen in FIG. 1, there will be severalpoints 13 (only a few of which are labeled) where the optical waveguidescross each other.

Unfortunately, each crossing adds an insertion loss (IL) to thethroughput of the corresponding optical path, which is undesirable. Itis known that a typical waveguide crossing loss is around 0.05 dB percrossing. As can be seen in FIG. 1, it is also apparent that the numberof crossings will vary greatly: from none in the outer paths to(M−1)*(N−1) for some of the inner paths. This will lead to paths withhigher insertion loss, which increases both the worst-case insertionloss as well as the insertion loss uniformity (ILU) of all of the pathsin the switch 10.

Moreover, some of the light within one waveguide can be transferred to acrossing waveguide if the angle between the two waveguides is too low.As can be appreciated, the mesh gets more and more complicated as thenumber of splitters 12 and switches 14 increase, which leads to lowerangles in some of the crossings. This situation is also undesirablebecause the overall isolation of the multicast switch 10 is degraded bythe light transfer.

FIG. 2 illustrates an example 4×4 multicast switch 20 using a mesh 26 ofoptical waveguides to connect the outputs of splitters 22 to the inputsof switches 24. The outside paths such as path 23 ₁ has no crossings,while the other paths (e.g., path 23 ₂) can have can have up to ninecrossings each. This means that the mesh 26 used in switch 20experiences insertion loss anywhere from 0 to about 0.45 dB per opticalpath, which as noted above is undesirable.

FIG. 3 illustrates an example 8×8 multicast switch 30 using a mesh 36 ofoptical waveguides to connect the outputs of splitters 32 to the inputsof switches 34. The outside paths such as path 33 ₁ has no crossings,while the other paths (e.g., path 33 ₂) can have can have up toforty-nine crossings. This means that the mesh 36 used in switch 30experiences insertion loss anywhere from 0 to about 2.45 dB per opticalpath. As can be seen, the FIG. 3 mesh 36 is much more complex than theFIG. 2 mesh 20, which leads to the greater insertion loss as well as lowcrossing angles (and potential crosstalk) in some of its paths.

There have been attempts to overcome similar problems in the past forother types of optical switches. For example, U.S. Pat. No. 4,787,692discloses an optical switching element comprising multiple stages ofactive switches interconnected by optical waveguides. In one embodiment,the architecture of the '692 patent has four regions of crossovers, andother regions of switches. This arrangement, however, is still notsuitable for today's needs.

U.S. Pat. No. 4,852,958 discloses an optical matrix switch comprising atree-type structure having an input branching tree connected to anoutput merging tree through a stage of 2×2 switches, waveguides anddummy waveguides. The disclosed architecture is still complex, still hascrossovers and requires active switches in addition to waveguide anddummy waveguide connections.

Jajszczyk et al., “Tree-type Photonic Switching Networks”, IEEE Network,vol. 9 no. 1 pp. 10-16 (1995), discloses various tree-type architecturesfor photonic switching networks, included guided-wave based switchingelements. Each architecture has its advantages and disadvantages, usesdifferent amounts of active elements, and experiences different types ofcrossovers, insertion loss, and signal-to-noise ratios. The disclosedarchitectures, however, do not reduce the number of crossings enough fortoday's technological requirements.

Thus, there remains a need to further reduce the number of waveguidecrossings in optical switches such as M×N multicast switches and otherM×N optical components.

SUMMARY

An embodiment disclosed herein provides an optical switching elementcomprising a first stage having M inputs and being adapted to split eachinput into N first stage outputs, wherein M and N are integers greaterthan one; and a second stage connected to the first stage outputs andhaving N outputs, said second stage comprising at least first and secondwaveguide areas and at least first and second output switch areas. Thefirst waveguide area comprises a plurality of waveguides connectedbetween the first stage outputs and inputs of switches in the firstoutput switch area, and the second waveguide area comprises a pluralityof waveguides connected between outputs of the switches in the firstoutput switch area and inputs of switches in the second output switcharea. The waveguides in the first and second waveguide areas cross otherwaveguides in the same waveguide area in respective sets of waveguides,wherein each set comprises two or more waveguides.

Another embodiment disclosed herein provides an optical network elementcomprising M inputs and N outputs, said optical network elementcomprising at least one stage comprising a plurality of waveguide areas,wherein waveguides within each waveguide area cross other waveguides inthe same waveguide area in sets of waveguides.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, drawings and claims providedhereinafter. It should be understood that the detailed description,including disclosed embodiments and drawings, are merely exemplary innature intended for purposes of illustration only and are not intendedto limit the scope of the invention, its application or use: Thus,variations that do not depart from the gist of the invention areintended to be within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates an example M×N multicast switch comprising M 1×Nsplitters and N M×1 switches.

FIG. 2 illustrates an example 4×4 multicast switch using opticalwaveguides to connect the outputs of splitters to the inputs ofswitches.

FIG. 3 illustrates an example 8×8 multicast switch using opticalwaveguides to connect the outputs of splitters to the inputs ofswitches.

FIG. 4 illustrates an example 4×4 multicast switch using opticalwaveguides constructed in accordance with the disclosed principles.

FIG. 5 illustrates an example 8×8 multicast switch using opticalwaveguides constructed in accordance with the disclosed principles.

FIG. 6 is a graph comparing the number of waveguide crossings in aswitch constructed in accordance with the disclosed principles to aswitch constructed in accordance with the convention technique.

FIG. 7 illustrates an example of M×N optical switch constructed inaccordance with the disclosed principles.

FIG. 8 illustrates another example of M×N optical switch constructed inaccordance with the disclosed principles.

FIG. 9 illustrates yet another example M×N optical switch constructed inaccordance with the disclosed principles.

FIG. 10 illustrates an example of M×N optical splitter constructed inaccordance with the disclosed principles.

DETAILED DESCRIPTION

As will become apparent from the following description, the embodimentsdisclosed herein provide new architectures for multicast switches, andother optical switches and splitters, that have substantially reducedinsertion loss, crosstalk and better overall optical performance incomparison to existing optical switches and splitters. The embodimentsdisclosed herein feature optimized waveguide mesh layouts thatsubstantially reduce waveguide crossings, which reduces insertion loss.The reduction in crossings also reduces the complexity of the mesh andprovides better crossing angles to reduce crosstalk and other issues.Instead of crossing all of the waveguides connected between splitteroutputs and switch inputs, the waveguides are crossed in sets ofwaveguides, which dramatically reduces the number of crossings and theproblems associated thereto.

FIG. 4 illustrates an example 4×4 multicast switch 120 constructed inaccordance with the disclosed principles. In this embodiment, the numberM of inputs is four and the number N of outputs is four. The switch 120includes four 1×4 splitters 122 serving as an input stage of the switch120. The first stage is connected to a second stage comprising a firstmesh area 126 _(a), a first switch area 124 _(a), a second mesh area 126_(b), and a second switch area 124 _(b). In a desired embodiment, all ofthe components in the switch 120 are connected to or part of the samesubstrate. The first switch area 124 _(a) comprises eight 2×1 switches125 ₁, . . . , 125 ₈. The second switch area 124 _(b) comprises four 2×1switches 125 ₉, . . . , 125 ₁₂. In one embodiment, the switches 125 ₁, .. . , 125 ₁₂ are Mach-Zehnder (MZ) switches. It should be appreciatedthat any suitable 2×1 switch can be used for the switches 125 ₁, . . . ,125 ₁₂, MZ switches being one example that can be used in theillustrated embodiment.

The first mesh area 126 _(a) comprises sixteen waveguides 129 ₁, . . . ,129 ₁₆, each having one end connected to a respective output of one ofthe splitters 122. The other ends of the waveguides 129 ₁, . . . , 129₁₆ are respectively connected to one of the inputs of the switches 125₁, . . . , 125 ₈ of the first switch area 124 _(a). The second mesh area126 _(b) comprises eight waveguides 129 ₁₇, . . . , 129 ₂₄, each havingone end connected to a respective output of one the switches 125 ₁, . .. , 125 ₈ of the first switch area 124 _(a). The other ends of thewaveguides 129 ₁₇, . . . , 129 ₂₄ are respectively connected to one ofthe inputs of the switches 125 ₉, . . . , 125 ₁₂ of the second switcharea 124 _(b). A control mechanism (not shown) ensures that the switches125 ₉, . . . , 125 ₁₂ are set to output the correct signal duringoperation of the switch 120.

Unlike the waveguides used in the meshes 26, 36 illustrated in FIGS. 2and 3, the waveguides 129 ₁, . . . , 129 ₂₄ in the first and second meshareas 126 _(a), 126 _(b) are crossed in sets 127 ₁, 127 ₂, 127 ₃, 127 ₄,127 ₅, 127 ₆ of waveguides. In the illustrated embodiment, sets 127 ₁crosses with set 127 ₂, set 127 ₃ crosses with set 127 ₄, and set 127 ₅crosses with set 127 ₆. In the illustrated embodiment, the number ofwaveguides in each set 127 ₁, 127 ₂, 127 ₃, 127 ₄, 127 ₅, 127 ₆ is four,matching the number N of outputs from the switch 120. It should beappreciated, however, that even though the waveguides 129 ₁, . . . , 129₂₄ are grouped into sets 127 ₁, 127 ₂, 127 ₃, 127 ₄, 127 ₅, 127 ₆, andeach set 127 ₁, 127 ₂, 127 ₃, 127 ₄, 127 ₅, 127 ₆ crosses with anotherset, one waveguide in each set will not cross another waveguide as thatwaveguide will already be in proper position for its connection to aswitch (e.g., waveguides 129 ₁, 129 ₁₆, 129 ₁₇, 129 ₂₄ do not crossother waveguides even though they are part of a set).

The largest number of crossings is reduced from (N−1)×(M−1) to (N−1)×log2 (M). For example, in the illustrated embodiment, the 4×4 switch 120can have at most six crossings instead of the nine crossings experiencedby paths in the mesh 26 illustrated in FIG. 2. Six crossings would onlyresult in about a 0.3 dB loss, which is a substantial improvement overprior 4×4 multicast and other switches. In addition, the reduction inthe number of crossings makes the mesh areas 126 _(a), 126 _(b) lesssusceptible to crosstalk as larger crossing angles can be achieved dueto less congestion in these areas. This is another benefit over priormulticast and other switches.

FIG. 5 illustrates an example 8×8 multicast switch 130 constructed inaccordance with the disclosed principles. In this embodiment, the numberM of inputs is eight and the number N of outputs is eight. The switch130 includes eight 1×8 splitters 132 serving as a first stage of theswitch 130. The first stage is connected to a second stage comprising afirst mesh area 136 _(a), a first switch area 134 _(a), a second mesharea 136 _(b), a second switch area 134 _(b), a third mesh area 136_(c), and a third switch area 134 _(c). In a desired embodiment, all ofthe components in the switch 130 are connected to or part of the samesubstrate. The first switch area 134 _(a) comprises thirty-two 2×1switches 135 ₁, . . . , 135 ₃₂. The second switch area 134 _(b)comprises sixteen 2×1 switches 135 ₃₃, . . . , 135 ₄₈ and the thirdswitch area 134 _(c) comprises eight 2×1 switches 135 ₄₉, . . . , 135₅₆. In one embodiment, the switches 135 ₁, . . . , 135 ₅₆ are MZswitches. It should be appreciated that any suitable 2×1 switch can beused for the switches 135 ₁, . . . , 135 ₅₆, MZ switches being oneexample that can be used in the illustrated embodiment.

The first mesh area 136 _(a) comprises sixty-four waveguides 139 ₁, . .. , 139 ₆₄, each having one end connected to a respective output of oneof the splitters 132. The other ends of the waveguides 139 ₁, . . . ,139 ₆₄ are respectively connected to one of the inputs of the switches135 ₁, . . . , 125 ₃₂ of the first switch area 134 _(a). The second mesharea 136 _(b) comprises thirty-two waveguides 139 ₆₅, . . . , 139 ₉₆,each having one end connected to a respective output of one the switches135 ₁, . . . , 135 ₃₂ of the first switch area 134 _(a). The other endsof the waveguides 139 ₆₅, . . . , 139 ₉₆ are respectively connected toone of the inputs of the switches 135 ₃₃, . . . , 135 ₄₈ of the secondswitch area 134 _(b). The third mesh area 136 _(c) comprises sixteenwaveguides 139 ₉₇, . . . , 139 ₁₁₂, each having one end connected to arespective output of one the switches 135 ₃₃, . . . , 135 ₄₈ of thesecond switch area 134 _(b). The other ends of the waveguides 139 ₉₇, .. . , 139 ₁₁₂ are respectively connected to one of the inputs of theswitches 135 ₄₉, . . . , 135 ₅₆ of the third switch area 134 _(c). Acontrol mechanism (not shown) ensures that the switches 135 ₄₉, . . . ,135 ₅₆ are set to output the correct signal during operation of theswitch 130.

Unlike the waveguides used in the meshes 26, 36 illustrated in FIGS. 2and 3, the waveguides 139 ₁, . . . , 139 ₁₁₂ in the first, second andthird mesh areas 136 _(a), 136 _(b), 136 _(c) are crossed in sets 137 ₁,137 ₂, . . . , 137 ₁₃, 137 ₁₄ of waveguides. For example, set 137 ₁crosses with set 137 ₂, set 137 ₇ crosses with set 137 ₈, set 137 ₉crosses with set 137 ₁₀, set 137 ₁₁ crosses with set 137 ₁₂, and sets137 ₁₃ crosses set 137 ₁₄. In the illustrated embodiment, the number ofwaveguides in each set 137 ₁, 137 ₂, . . . , 137 ₁₃, 137 ₁₄ is eight,matching the number N of outputs from the switch 130. It should beappreciated, however, that even though the waveguides 139 ₁, . . . , 139₁₁₂ are grouped into sets 137 ₁, . . . , 137 ₁₄, and each set 137 ₁, . .. , 137 ₁₄ crosses with another set, one waveguide in each set will notcross another waveguide as that waveguide will already be in properposition for its connection to a switch (e.g., waveguides 139 ₁, 139 ₆₄,139 ₆₅, 139 ₉₆,139 ₉₇ and 139 ₁₁₂ do not cross other waveguides eventhough they are part of a set).

The largest number of crossings is reduced from (N−1)×(M−1) to (N−1)×log2 (M). For example, in the illustrated embodiment, the 8×8 switch 130can have at most twenty-one crossings instead of the forty-ninecrossings experienced by paths in the mesh 36 illustrated in FIG. 3.Twenty-one crossings would only result in about a 1.05 dB loss, which isa substantial improvement over prior 8×8 multicast and other switches.In addition, the reduction in the number of crossings makes the meshareas 136 _(a), 136 _(b), 136 _(c) less susceptible to crosstalk aslarger crossing angles can be achieved due to less congestion in theseareas. This is another benefit over prior multicast and other switches.

As can be seen, the disclosed techniques provides the switches 120, 130with simple layouts regardless of the number of splitters and switchesused. There is also substantially less crossings than the conventionaltechnique illustrated in FIGS. 2 and 3. FIG. 6 is a graph comparing thenumber of waveguide crossings in a switch constructed in accordance withthe disclosed principles (i.e., FIGS. 4 and 5) to a switch constructedin accordance with the conventional technique (i.e., FIGS. 2 and 3).Line 201 illustrates the crossings of switches constructed in accordancewith the disclosed principles (i.e., log 2 (M)) while line 203illustrates the crossings of switches constructed in accordance with theconventional technique (i.e., (N−1)).

It should be noted that the disclosed embodiments have been describedwith reference to multicast switches having the same number M of inputsas the number N of outputs. Moreover, the embodiments have been shownwith use of passive splitter/active combiner (PS/AC) configurations. Itshould be appreciated, however, that the disclosed principles are notlimited to these types of switches or configurations. For example, theswitch can comprise less than 4 inputs and/or outputs or more than eightinputs and/or outputs. Other example embodiments will now be describedto reflect further applications of the disclosed principles.

FIG. 7 illustrates an example of 4×8 multicast switch 300 constructed inaccordance with the disclosed principles. The disclosed switch 300includes four 1×4 splitters 322 serving as a first stage of the switch300, which is connected to a second stage comprising a first mesh area326 _(a), a first switch area 324 _(a), a second mesh area 326 _(b), anda second switch area 324 _(b). In a desired embodiment, all of thecomponents in the switch 300 are connected to or part of the samesubstrate. The first switch area 324 _(a) comprises sixteen 2×1 switches325 ₁, . . . , 325 ₁₆. The second switch area 324 _(b) comprises eight2×1 switches 325 ₁₇, . . . , 325 ₂₄. As with the other disclosedembodiments, the switches 325 ₁, . . . , 325 ₂₄ can be, but are notlimited to, Mach-Zehnder (MZ) switches.

The first mesh area 326 _(a) comprises thirty-two waveguides 329 ₁, . .. , 329 ₃₂, each having one end connected to a respective output of oneof the splitters 322. The other ends of the waveguides 329 ₁, . . . ,329 ₃₂ are respectively connected to one of the inputs of the switches325 ₁, . . . , 325 ₁₆ of the first switch area 324 _(a). The second mesharea 326 _(b) comprises sixteen waveguides 329 ₃₃, . . . , 329 ₄₈, eachhaving one end connected to a respective output of one the switches 325₁, . . . , 325 ₁₆ of the first switch area 324 _(a). The other ends ofthe waveguides 329 ₃₃, . . . , 329 ₄₉ are respectively connected to oneof the inputs of the switches 325 ₁₇, . . . , 325 ₂₄ of the secondswitch area 324 _(b).

As in the other disclosed embodiments, the waveguides 329 ₁, . . . , 329₄₈ in the first and second mesh areas 326 _(a), 326 _(b) are crossed insets 327 ₁, 327 ₂, 327 ₃, 327 ₄, 327 ₅, 327 ₆ of waveguides. In theillustrated embodiment, sets 327 ₁ crosses with set 327 ₂, set 327 ₃crosses with set 327 ₄, and set 327 ₅ crosses with set 327 ₆. In theillustrated embodiment, the number of waveguides in each set 327 ₁, 327₂, 327 ₃, 327 ₄, 327 ₅, 327 ₆ is eight, matching the number N of outputsfrom the switch 300. It should be appreciated, however, that even thoughthe waveguides 329 ₁, . . . , 329 ₄₈ are grouped into sets 327 ₁, 327 ₂,327 ₃, 327 ₄, 327 ₅, 327 ₆, and each set 327 ₁, 327 ₂, 327 ₃, 327 ₄, 327₅, 327 ₆ crosses another set, one waveguide in each set will not crossanother waveguide as that waveguide will already be in proper positionfor its connection to a switch (e.g., waveguides 329 ₁, 329 ₃₂, 329 ₃₃,329 ₄₈ do not cross other waveguides even though they are part of aset).

In this embodiment, the 4×8 multicast switch 300 will have at most(N−1)×log 2 (M) crossings. That is, with the number M of inputs beingfour and the number N of outputs being eight, the worst case crossingwill be (8−1)×log 2 (4) or 14. The convention method would have up to(8−1)×(4−1) or 21 crossings.

FIG. 8 illustrates another example of a 4×8 multicast switch 400constructed in accordance with the disclosed principles. In the FIG. 8embodiment, waveguide mesh areas 422 _(a), 422 _(b) and 422 _(c) areused as in a splitter area instead of being used in the switch area asshown in prior embodiments. In a desired embodiment, all of thecomponents in the switch 400 are connected to or part of the samesubstrate. As there are four inputs into the switch 400, the waveguideswithin the mesh areas 422 _(a), 422 _(b) and 422 _(c) are crossed insets of four (additional notations are not present in FIG. 8 to preventcluttering of the figure). The first mesh area 422 _(a) splits in to thesecond mesh area 422 _(b) via crossings of sets of four waveguides. Thesecond mesh area 422 _(b) splits in to the third mesh area 422 _(c) viaadditional crossings of sets of four waveguides. The waveguides of thethird mesh area 422 _(c) cross in sets of four waveguides, which areconnected to the inputs of the switch area 424. The outputs of theswitch area 424 serve as the outputs of the switch 400. The illustrated4×8 switch 400 will have a maximum of 9 crossings (i.e., (4−1)×log 2(8)), which is even more advantageous than the FIG. 7 switch 300.

It should also be appreciated that other types of switches and splitterscan benefit from a similar waveguide arrangement

FIG. 9 illustrates a 4×8 optical switch 500 that is not a multicastswitch. The switch 500 includes five switch areas 510 _(a), 510 _(b),510 _(c), 510 _(d), 510 _(e) and three waveguide mesh areas 520 _(a),520 _(b), 520 _(c). In a desired embodiment, all of the components inthe switch 500 are connected to or part of the same substrate. The firstswitch area 510 _(a) comprises four 1×2 switches connected to one offour inputs to the switch 500. Outputs of the switches from the firstswitch area 510 _(a) are connected to one of the waveguides in the firstmesh area 520 _(a). As can be seen, the waveguides in the first mesharea 520 _(a) are crossed in sets 530 ₁, 530 ₂ of four waveguides. Theother ends of the waveguides in the first mesh area 520 _(a) areconnected to respective inputs of 1×2 switches in the second switch area510 _(b).

The outputs of the switches second switch area 510 _(b) are connected toa respective one of the waveguides in the second mesh area 520 _(b). Ascan be seen, the waveguides in the second mesh area 520 _(b) are alsocrossed in sets 530 ₃, 530 ₄, 530 ₅, 530 ₆ of four waveguides. The otherends of the waveguides in the second mesh area 520 _(b) are connected torespective inputs of 1×2 switches in the third switch area 510 _(c). Theoutputs of the switches in the third switch area 510 _(c) are connectedto a respective one of the waveguides in the third mesh area 520 _(c).The waveguides in the third mesh area 520 _(c) are also crossed in sets530 ₇, . . . , 530 ₁₄ of four waveguides. The other ends of thewaveguides in the third mesh area 520 _(c) are connected to respectiveinputs of 2×1 switches in the fourth switch area 510 _(d). Outputs ofthe switches in the fourth switch area 510 _(d) are connected torespective inputs of the inputs to 2×1 switches in the fifth switch area510 _(e). The outputs from the switches in the fifth switch area 510_(e) comprise the outputs of the switch 500.

It should be appreciated that the switch 500 achieves similar crossingreductions as discussed above with respect to other embodimentsdisclosed herein. Likewise, the reduction of crossings reduces thecomplexity of the switch 500, leaving room for larger crossing angleswhere crossings are required, which reduces crosstalk in the switch. Itshould also be appreciated that the novel features of the embodiment arenot limited to a 4×8 switch and that any number of inputs and outputs(along with the appropriate mesh areas and switches) could be used.

FIG. 10 illustrates a 4×8 splitter 600 constructed in accordance withanother disclosed embodiment. The splitter 600 has four waveguide meshareas 610 a, 610 b, 610 c, 610 d and a switch 620. In a desiredembodiment, all of the components in the splitter 600 are connected toor part of the same substrate. The first mesh area 610 a comprises fourwaveguides connected as inputs into the splitter 600. The waveguides ofthe first mesh area 610 a split in to the second mesh area 610 _(b) viacrossings of sets of four waveguides. The second mesh area 610 _(b)splits in to the third mesh area 610 _(c) via additional crossings ofsets of four waveguides. The third mesh area 610 _(c) splits in to thefourth mesh area 610 _(d) via additional crossings of sets of fourwaveguides. The waveguides of the fourth mesh area 610 _(d) areconnected to the inputs of the switch area 620. The outputs of theswitch area 620 serve as the outputs of the splitter 600.

It should be appreciated that the splitter 600 achieves similar crossingreductions and crosstalk reductions as discussed above with respect tothe switch embodiments disclosed herein. It should also be appreciatedthat the novel features of the embodiment are not limited to a 4×8splitter and that any number of inputs and outputs (along with theappropriate mesh areas and switches) could be used. Moreover, as shownabove, the techniques of the disclosed embodiments can also be appliedto active splitter/active combiner (AS/AC) and passive splitter/passivecombiner (PS/PC) architectures.

The foregoing examples are provided merely for the purpose ofexplanation and are in no way to be construed as limiting. Whilereference to various embodiments is made, the words used herein arewords of description and illustration, rather than words of limitation.Further, although reference to particular means, materials, andembodiments are shown, there is no limitation to the particularsdisclosed herein. Rather, the embodiments extend to all functionallyequivalent structures, methods, and uses, such as are within the scopeof the appended claims.

Additionally, the purpose of the Abstract is to enable the patent officeand the public generally, and especially the scientists, engineers andpractitioners in the art who are not familiar with patent or legal termsor phraseology, to determine quickly from a cursory inspection thenature of the technical disclosure of the application. The Abstract isnot intended to be limiting as to the scope of the present inventions inany way.

What is claimed is:
 1. An optical switching element comprising: a firststage having M inputs and being adapted to split each input into N firststage outputs, wherein M and N are integers greater than one; and asecond stage connected to the first stage outputs and having N outputs,said second stage comprising at least first and second waveguide areasand at least first and second output switch areas, the first waveguidearea comprising a plurality of waveguides connected between the firststage outputs and inputs of switches in the first output switch area,the second waveguide area comprising a plurality of waveguides connectedbetween outputs of the switches in the first output switch area andinputs of switches in the second output switch area, wherein thewaveguides in the first and second waveguide areas cross otherwaveguides in the same waveguide area in respective sets of waveguides,each set comprising two or more waveguides.
 2. The optical switchingelement of claim 1, wherein M is four and N is four and the waveguidesin the first and second waveguide areas cross the other waveguides inthe same waveguide areas in respective sets of four waveguides.
 3. Theoptical switching element of claim 1, wherein M is eight and N is eightand said second stage further comprises a third waveguide areacomprising a plurality of waveguides connected between outputs of theswitches in the second output switch area and inputs of switches in athird output switch area, and wherein the waveguides in the first,second and third waveguide areas cross other waveguides in the samewaveguide area in respective sets of eight waveguides.
 4. The opticalswitching element of claim 1, wherein M is four and N is eight and thewaveguides in the first and second waveguide areas cross otherwaveguides in the same waveguide area in respective sets of eightwaveguides.
 5. The optical switching element of claim 1, wherein M isfour and N is eight and said second stage further comprises a thirdwaveguide area comprising a plurality of waveguides connected betweenoutputs of the switches in the second output switch area and inputs ofswitches in a third output switch area, and wherein the waveguides inthe first, second and third waveguide areas cross other waveguides inthe same waveguide area in respective sets of four waveguides.
 6. Theoptical switching element of claim 1, wherein a number of waveguidecrossings for a given waveguide path is at most (N−1)×log 2 (M).
 7. Anoptical network element comprising M inputs and N outputs, said opticalnetwork element comprising: at least one stage comprising a plurality ofwaveguide areas, wherein waveguides within each waveguide area crossother waveguides in the same waveguide area in sets of waveguides. 8.The optical network element of claim 7, wherein the waveguides withineach waveguide area cross other waveguides in the same waveguide area insets of N waveguides.
 9. The optical network element of claim 7, whereinthe waveguides within each waveguide area cross other waveguides in thesame waveguide area in sets of M waveguides.
 10. The optical networkelement of claim 7, wherein the optical element is an M×N multicastswitch.
 11. The optical network element of claim 7, wherein the opticalelement is an M×N optical switch.
 12. The optical network element ofclaim 7, wherein the optical element is an M×N splitter.
 13. The opticalnetwork element of claim 7, wherein a number of waveguide crossings fora given waveguide path is at most (N−1)×log 2 (M).
 14. An opticalnetwork element comprising: a first stage having M inputs and aplurality of first stage outputs; and a second stage connected to theplurality of first stage outputs and having N outputs, said second stagecomprising first and second waveguide areas and first and second outputareas, the first waveguide area comprising a plurality of waveguidesconnected between the first stage outputs and inputs of the first outputarea, the second waveguide area comprising a plurality of waveguidesconnected between outputs of the first output area and inputs of thesecond output, wherein waveguide crossings occur in sets of waveguidescomprising more than 1 waveguide.
 15. The optical switching element ofclaim 14, wherein M is four and N is four and the waveguides in thefirst and second waveguide areas cross other waveguides in the samewaveguide area in respective sets of four waveguides.
 16. The opticalswitching element of claim 14, wherein M is eight and N is eight andsaid second stage further comprises a third waveguide area comprising aplurality of waveguides connected between outputs of the second outputarea and inputs of a third output area, and the waveguides in the first,second and third waveguide areas cross other waveguides in the samewaveguide area in respective sets of eight waveguides.
 17. The opticalswitching element of claim 14, wherein M is four and N is eight and thewaveguides in the first and second waveguide areas cross otherwaveguides in the same waveguide area in respective sets of eightwaveguides.
 18. The optical switching element of claim 14, wherein M isfour and N is eight and said second stage further comprises a thirdwaveguide area comprising a plurality of waveguides connected betweenoutputs of the second output area and inputs of a third output area, andthe waveguides in the first, second and third waveguide areas crossother waveguides in the same waveguide area in respective sets of fourwaveguides.
 19. The optical switching element of claim 14, wherein anumber of waveguide crossings for a given waveguide path is at most(N−1)×log 2 (M).